U.S – A recent study has shed light on the formation and characteristics of persister cells in Listeria monocytogenes, a bacterium of public health concern, particularly in produce packinghouse environments.

These persister cells are a subpopulation of growth-arrested cells known for their ability to tolerate antimicrobial agents and pose a risk of reverting to an active state under favorable conditions.

The study involved isolating 34 strains of L. monocytogenes from produce processing plants and packinghouses in California.

Through a fluorescent microplate adherence assay, three strains displaying the strongest adherence abilities were selected for further experimentation.

Investigating the impact of physiological status, cell density, and nutrient availability on persister cell formation, the researchers subjected the strains to various culture preparation methods.

Interestingly, differences in physiological status resulting from plate-grown versus broth-grown cultures did not significantly affect persister formation. However, a higher density of cells led to an increased ratio of persister cells.

To simulate packinghouse conditions, the researchers artificially inoculated stainless steel coupons with L. monocytogenes strains suspended in media with decreasing nutrient levels.

These nutrient-poor conditions included brain heart infusion broth, produce-washing water with varying organic loads, and sterile Milli-Q water.

Remarkably, the pathogen survived in all suspensions at a temperature of 4 °C and relative humidity of 85% for seven days. However, in nutrient-poor media, two of the three strains exhibited a decline in persister cell levels over time, indicating the influence of available nutrients on persister formation.

The study also evaluated the sensitivity of L. monocytogenes persister cells to chlorine treatment, comparing them with regular L. monocytogenes cells.

Despite their increased tolerance to the antibiotic gentamicin, the persister cells demonstrated greater susceptibility to chlorine treatment.

When exposed to a chlorine concentration of 100 mg/L for 2 minutes, the persister cells displayed a higher susceptibility compared to their regular counterparts.

This research provides valuable insights into the formation and characteristics of L. monocytogenes persister cells under produce packinghouse conditions.

The findings highlight the importance of understanding persister cells’ antimicrobial tolerance and their response to different treatment methods, such as chlorine disinfection. Such knowledge can contribute to the development of improved strategies for controlling L. monocytogenes and minimizing the risk of foodborne illnesses.

Listeria monocytogenes is a foodborne pathogen responsible for causing listeriosis, a potentially severe illness, especially among vulnerable populations.

The study’s findings emphasize the need for comprehensive food safety measures in produce processing and packinghouse environments to mitigate the risk of L. monocytogenes contamination.

Further research and innovation are crucial to enhance the efficacy of antimicrobial treatments and develop targeted control measures against persister cells in food production settings.

Ongoing research focuses on the development of novel antimicrobial strategies and technologies to combat persistent bacterial cells in various settings, including food processing.

Efforts are being made by regulatory agencies and industry stakeholders to strengthen food safety regulations and guidelines, placing emphasis on effective sanitation practices and the prevention of bacterial contamination in the food supply chain.

The study’s findings may contribute to the advancement of best practices and guidelines for cleaning and disinfection procedures in packinghouse facilities, enhancing food safety standards across the industry.

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